Rising expectations for magnetic nanoparticles for cancer diagnosis

Currently, X-ray CT and MRI are common methods for image diagnosis of diseases such as cancer. These methods show the difference in density of pictured objects in contrast. In recent years, image resolution has become very high, and an object smaller than 1 mm can be imaged.

However, the contrast of 1 mm objects is hardly recognizable with the naked eye that sees the objects, and in the case of a cancerous tumor, it is difficult to find a tumor unless the tumor is 1-3 cm.

Therefore, in recent years, a technique called molecular imaging has been developed. For example, with this technique, for studying cancer, substances called tracers that are designed to gather around cancer cells are administered into a body, and cancer is found by checking where the tracers have gathered.

Nanoparticles are used as tracers. Nano refers to a unit the size of one millionth of a millimeter, and in general, particles smaller than 100 nanometers are used as tracers in research in many countries.

Magnetic nanoparticles use a type of iron as material, and they are literally nanoparticles that have magnetic properties.

Substances that easily gather around cancer cells are made to surround the magnetic nanoparticles. Such magnetic nanoparticles are made into a solution and administered into the body by intravenous injection. Because of the characteristics of the substances surrounding the magnetic nanoparticles, the magnetic nanoparticles circulating in the body approach cancer cells.

Normal cells try to flush out foreign substances that have entered, but the function of cancer cells for flushing out foreign substances is inactive, and thus the magnetic nanoparticles accumulate in cancer cells.

Therefore, if a place where the magnetic nanoparticles are gathering is detected, the positions of the cancer cells can be found.

That is, compared to an image diagnosis in which it is difficult to discover a cancerous tumor unless the cancerous tumor becomes 1 cm or larger, early discovery of cancer at the cell level is possible.

In fact, for molecular imaging, there is a technique using, as tracers, not only magnetic nanoparticles, but nanoparticles of substances that have the characteristics of emitting radiation or emitting fluorescence. However, each technique has its own problem.

Substances emitting radiation have the problem of radiation exposure. In the case of fluorescent substances, detection is difficult unless the substances are close to the body’s surface.

In that respect, in the case of magnetic nanoparticles, since a magnet that is used is about the same as a contrast medium used for MRI, there is no problem like that of radiation exposure. Furthermore, as for detection, since a magnetic field is applied from outside the body for examination, detection is possible no matter where in the body the magnetic nanoparticles are located.

In other words, the magnetic nanoparticles are more advantageous than other tracers. However, there is still a problem, and the reality is that this technique has not been put into practical use yet.

Our laboratory’s approach to overcome the problem

There are two major problems for magnetic nanoparticle imaging. One is that the detection device is large. The other is about ensuring safety to living bodies.

In order to detect magnetic nanoparticles in a body, a magnetic field is applied from outside the body. However, it is said that examining the entire body requires a device as large as a current MRI scanner. In addition, coils and a power source are required for producing a magnetic field, and thus the entire device becomes very large.

A research group in Germany has built a small system for animals and started verifying the effectiveness in animal experiments. However, increasing the size of the device has been a problem for putting this system into practical application, and the clinical system has not yet been applied.

Therefore, a research group in America has made a device for examining only the head region of a human being and has been carrying out experiments. However, the problem of covering the wholebody has yet to be solved.

The other problem, which is about safety to living bodies, is that when a magnetic field is applied, stimulations are given to the living body and heat is generated.

In fact, for application of magnetic nanoparticles to medical care of cancer, medical treatment of cancer has been antecedently studied. When electromagnetic waves are applied to a region where magnetic nanoparticles accumulate, this region becomes extremely hot. The treatment is to kill cancer cells with this heat. That is the extent to which the energy of electromagnetic waves can become thermal energy.

Normal cells in which magnetic nanoparticles do not accumulate do not get this hot, but still generate heat. Such heat generation may affect the living body.

In order to overcome these problems, our laboratory has first miniaturized the device for detecting magnetic nanoparticles and has been working to develop, with such a small device, a method for accurately obtaining data and a technique for producing correct images from the data.

Moreover, we have been working to develop a technique for locating the positions of magnetic nanoparticles by vibrating the magnetic nanoparticles using ultrasonic waves and receiving signals emitted by vibrating magnets, instead of applying a magnetic field for detection of magnetic nanoparticles.

We have a long way to go to put our research into practical use, but we believe that, together with research institutions in many different countries, coming up with and sharing various ideas and repeating trial and error will lead to contributions to new discoveries and technological progress.

Results of accumulated attempts and ideas

Small attempts and ideas have often, when they are looked back upon, greatly contributed to technological progress and implementation, and application to other fields.

In fact, as mentioned earlier, application of magnetic nanoparticles was originally considered as a treatment of cancer, and now it is going to be used for early discovery of cancer.

Further, since magnetic nanoparticles are given by intravenous injection, if the magnetic nanoparticles are traced, abnormalities of blood flows can be detected, and research that can be used for early diagnosis of various diseases caused by bloodstream disorders is being promoted.

Moreover, it is considered that the magnetic nanoparticle imaging of a head region carried out by the research group in America may be useful not only for diagnosis of cancer, but also for diagnosis of cerebrovascular disorder and dementia.

Our laboratory has been working on a noninvasive blood glucose level measurement method as another major research subjects.

The noninvasive blood glucose level measurement method refers to a technique for measuring the blood glucose level without sampling blood and has been studied all over the world since the 1970s.

This method is based on the idea of using glucose’s property of absorbing light energy, and knowing a blood glucose level by, for example, exposing a finger to light and measuring the light that passes through the finger. In fact, in an experiment using glucose solution put in a test tube, the concentration of glucose was successfully estimated.

However, when the blood glucose levels are measured with a living body noninvasively, measurement values vary, and results as accurate as those by sampling blood cannot be obtained.

It is considered that this is because blood contains an extremely large amount of water, and the water also absorbs light. Moreover, it is very difficult to measure and analyze accurately the light that has passed through a living body anyway.

Therefore, we are doing research with applied photoacoustic spectroscopy, which is a technique of analytical chemistry.

When absorbing light energy, glucose is turned into heat and expands. When the light is stopped, no energy is supplied and the glucose returns to its original size.

By repeating this, vibration sound is generated from the glucose which increases and decreases in size. By measuring the vibration sound, it is considered that a blood glucose level with high accuracy can be detected.

In Japan, apparently one out of seven people has diabetes, and some of those who have diabetes have to control their blood glucose levels by sampling blood three to four times a day. The burden on their bodies, sanitary risks, and inspection costs are not at all small.

If the noninvasive blood glucose level measurement method can be put into practical use, such burdens can be eliminated. However, the reality is that the method has not been put into practical use for nearly half a century. We are currently investigating a variety of new methods in which techniques from different fields are incorporated, not the method that has been thoroughly studied thus far.

The task for us, the researchers, is to be free from preconceived ideas, make attempts and come up with ideas, and continue to engage in trial and error. Such attempts often end in failure.

However, we should consider such an experience as just one more trial and error and try to come up with new ideas. New inventions and new discoveries that have surprised the world are the outcomes of repetition of such work.

We have a long way to go to put medical devices and systems into practical use. However, I want you to understand that the accumulation of such steady and basic research conducted by universities and applied research will lead to a successful outcome. Understanding this idea will help put the early diagnosis system for cancer and the noninvasive blood glucose level measurement method into practical use.

* The information contained herein is current as of May 2021.
* The contents of articles on Meiji.net are based on the personal ideas and opinions of the author and do not indicate the official opinion of Meiji University.
* I work to achieve SDGs related to the educational and research themes that I am currently engaged in.

Information noted in the articles and videos, such as positions and affiliations, are current at the time of production.